Pressure transducer

ABSTRACT

This invention relates to a pressure transducer which is able to operate in all types of environments, including normally adverse environments, to provide an accurate indication of pressure. The pressure transducer is able to provide accurate indications of relatively high pressures in one embodiment and of relatively low pressures in a second embodiment. The pressure transducer provides such accurate indications by varying the distance between two plates of a capacitor in accordance with the variations in the pressure to be measured. The pressure transducer is made by novel methods also included within this invention.

United States Patent [191 Brown 11 3,750,476 [451 Aug. 7, 1973 PRESSURETRANSDUCER [75] Inventor: Neil L. Brown, El Cajon, Calif.

[73] Assignee: The Bissett-Bermen Corporation,

Santa Monica, Calif.

[22] Filed: Sept. 25, 1967 [21] Appl. No.: 670,210

[52] US Cl 73/398 C [51] Int. Cl. G011 9/12 [58] Field of Search 73/398C; 317/246 [56] References Cited UNITED STATES PATENTS 2,944,199 5/1960Hudson 73/398 2,848,710 8/1958 Owen 73/398 3,195,028 7/1965 Werner ctal.... 73/398 3,292,059 12/1966 Woods 317/246 3,356,963 12/1967 Buck73/398 3,405,559 10/1968 Moffatt 73/398 Primary Examiner-S. ClementSwisher Attorney-Smyth, Roston & Pavitt [57] ABSTRACT This inventionrelates to a pressure transducer which is able to operate in all typesof environments, including normally adverse environments, to provide anaccurate indication of pressure. The pressure transducer is able toprovide accurate indications of relatively high pressures in oneembodiment and of relatively low pressures in a second embodiment. Thepressure transducer provides such accurate indications by varying thedistance between two plates of a capacitor in accordance with thevariations in the pressure to be measured. The pressure transducer ismade by novel methods also included within this invention.

6 Claims, 7 Drawing Figures PATENTED M13 7 i975 sum 1 or 2 PATENTED M 775 sum 2 OF 2 MW r N w w Z, draw 1 PRESSURE TRANSDUCER This applicationrelates to pressure transducers and more particularly to transducerswhich measure pressure by varying the value of a capacitor. Theinvention also relates to methods of producing such transducers.

As our technology advances, it becomes increasingly important to provideaccurate measurements of various parameters such as pressure. Thesemeasurements have to be accurate even when extraneous parameter such astemperature are varying considerably. The measurements have to beaccurate in various environments such as in air and in liquids. Themeasurements have to be accurate even in such liquids as sea water wherethe salinity of the sea water varies at different positions in the waterand where the salinity of the sea water tends to corrode the measuringinstruments.

Various attempts have been made to provide a pressure transducer whichcan operate to provide precise measurements of pressure under differentconditions. These pressure transducers have not been entirelysatisfactory for a number of reasons. One reason has been that thepressure transducers are generally not sealed so that their operatingeffectiveness becomes impaired when exposed tosuch adverse environmentsas sea water. Another reason hasbeen that the pressure transducers donot provide operating characteristics which vary linearly withvariations in pressure. A further problem has been that the pressuretransducers respond unfavorably to variations in such extraneousparameters as temperature.

This invention provides a pressure transducer which overcomes thedisadvantage discussed above. The pressure transducer is made from apair of members which are sealed to each other so that the operation ofthe pressure transducer is not adversely effected by such environmentssuch as sea water. The two members are disposed in a particularrelationship such as in uniformly spaced contiguity and are'coated withan electrically conductive material to define a pair of plates in acapacitor. The distance between the plates is varied in accordance withvariations in the pressure imposed upo one of the plates relative tothat imposed upon the other plate so that the value of the capacitancedefined by the plates also varies linearly. The members may be formed ascylindrical membershaving a concentric relationship in one embodimentand may be formed as uniformly spaced planar members in a secondembodiment. I

Preferably the two members discussed in the previous paragraph areformed from quartz since quartz provides certain important advantages.One advantage is that quartz is chemically inert so that it will notcorrode in adverse environments such as sea water. Furthermore, sincequartz is able to withstand considerable forces in compression, it canbe used to measure high pressures in the embodiment in which the twomembers have a concentric cylindrical relationship. Quartz also exhibitssubstantially no hysteresis characteristics when subjected to stressesor strains. This causes the operating characteristics of the transducersconstituting this invention to remain substantially constant regardlessof the stress or strain imposed upon the members unless the stress orstrain is of such great magnitude that the quartz becomes fractured.Another advantage is that quartz has a very low temperature coefficientof expansion so that its response to pressure is hardly affected bychanges in temperature.

In the embodiment where the two members have a concentric cylindricalrelationship relative to each other, the members are not affected to anyappreciable extent by any external capacitive fields since the membersare self-contained. This is especially true when the external surface ofthe outer member is coated with a conductive layer of material to serveas an electrical shield. However, in the embodiment where the twomembers have a planar relationship, novel means are provided forshielding the members capacitively from each other. Novel means are alsoprovided for electrical connections to the conductive coatings on eachof the two members to insure that the electrical connections will notaffect the value of the capacitor defined by the two coatings. Suchnovel means will be described subsequently in connection with a detaileddescription of the invention.

One of the features constituting this invention is the method of makingthe pressure transducers. This is particularly true with respect to theembodiment where the two quartz members have a substantially planarrelationship. In forming this embodiment, wires having a diametercorresponding to the desired spacing between the two quartz members areinserted between the members and the two members are then sealed to eachother. The wires are then removed from the space between the two quartzmembers since the two members are now fixedly disposed relative to eachother. The novel method also includes a novel way of making electricalconnections to the plates of the capacitor produced between the twoquartz members.

IN THE DRAWINGS FIG. I is a sectional view of one embodiment of apressure transducer constituting the invention;

FIG. 2 is a circuit diagram somewhat schematically illustrating a systemfor measuring the pressure indicated by the transducer shown in FIG. 1;

FIG. 3 is an enlarged sectional view schematically illustrating certainfeatures included in a second embodiment of the invention, the sectionbeing taken substantially on the line 3'3 of FIG. 4;

FIG. 4 is a plan view further illustrating features included in thesecond embodiment of the invention;

FIG. 5 is a plan view illustrating certain steps in a method of makingthe embodiment shown in FIGS. 3 and 4;

FIG. 6 is an elevational view, in section, illustrating other steps inthe method of making the embodiment shown in FIGS. 3 and 4 and furtherillustrating other features of the embodiment shown in FIGS. 3 and 4;and

FIG. 7 is a schematic diagram illustrating the electrical relationshipbetween different capacitors produced in the embodiment shown in FIGS. 3and 4.

In the embodiment of the invention illustrated in FIG. I, a tube 10 anda rod 12 are preferably provided with a cylindrical configuration andare made from a suitable material such as quartz. Quartz is advantageousfor a number of reasons. One reason is that it constitutes an electricalinsulator so that it is not affected electrically or chemically by saltand other chemical elements and compounds in adverse environments suchas sea water. It is also chemically inert so that it does not corrode inadverse environments such as sea water. Furthermore, quartz constitutesa pure compound from a chemical standpoint so that no chemical ormetallurgical variations exist at different positions in the quartz toaffect the operating characteristics at such positions.

Quartz is able to withstand a relatively great range of temperaturesfrom low temperatures to high temperatures without being adverselyaffected in its operating characteristics. It has a relatively lowtemperature coefficient of expansion such as in the order of 0.5 partsper million per degree centigrade. This prevents changes in ambienttemperature from adversely affecting the operating characteristics ofthe transducer. Quartz is almost elastically perfect so that it exhibitsno hysteresis when subjected to stress or strain below the limits whereit would fracture. It is also very strong when subjected to compression.This is important in the embodiment shown in FIG. 1 in view of the factthat the force or pressure is imposed in a radial direction against theannular surface of the tube 10.

The external diameter of the rodl2 at the left and right extremities ofthe rod in FIG. 1 corresponds to the internal diameter of the tube 10 sothat the rod 12 fits snugly within the tube 10. The end facesl4 andl6'of the rod 12 are sealed to the tube 10 at the opposite endsor'extremities of the tubes by applying heat to the tube l at theperipheries indicated at 20 and 22 in FIG. 1. The rod 14 is providedwith annular grooves 24 and 26 near its opposite ends to prevent suchheat from travelling axially along the tube and the rod l2 to seal therod to the tube along the annular portion of the rod and tube betweenthe ends 14 and 18. For example, it is undesirable to seal the rod andthe tube between the end face 14 and a position 30 indicated by a brokenline and between the end face 16 and a position 32 indicated by a brokenline.

The rod 12 is progressively tapered between the axial positions 30 and32. The taper occurs primarily in the area between the axial position 30and an axial position 36 indicated by a broken line and between theaxial position 32 and an axial position 38 indicated by a broken line.Between the axial positions 36 and 38, the rod 12 is provided with asubstantially cylindrical configura tion and is separated by arelatively small distance such as 0.005 inches from the inner peripheryof the tube 10.

The rod 12 is uniformly coated with a thin layer of a conductivematerial such as platinum in substantially all of its external peripherybetween the axial positions 36 and 38. The electrical conductive coating40 constitutes a first plate of a transducing capacitor generallyindicated at 42. The second plate of the capacitor 42 is formed byuniformly coating the internal periphery of the tube 10 with a thinlayer ofthe electrically conductive material such as platinum. Thiscoating is provided on substantially the complete internal periphery ofthe tube 10 between the axial positions 30 and 32 and is indicated at44. In this way, the coating 44 defines the second plate of thecapacitor 42. As will be seen, the coating 44 extends axially beyond thecoating 40 in the area between the axial positions 30 and 36 at one endand in the area between the axial positions 38 and 32 at the oppositeend. By causing the coating 44 to overlap the coating 40, electricalshielding is provided to insure that the capacitor 42 is not affected inoperation by extraneous capacitive or electrical fields.

A bore 46 extends axially through the rod from the end face 14 to aposition just beyond the axial position 36. The bore communicates at itsinternal extremity with the outer periphery of the rod 10. The bore iscoated with the conductive material along a wall 50 to communicate withthe coating 40, and an electrical connection is made as at 52 betweenthe conductive coating and an electrical lead 54 which extends throughthe bore 46 to a position external to the pressure transducer. In likemanner, a bore 56 is provided in the rod 12 between the end face 14 anda position adjacent to the axial position 30. This bore communicateswith the external periphery of the rod 12. An electrical connection ismade between the coating 44 on the internal surface of the tube 10 andan electrical lead 58 which extends through the bore 56 to a positionexternal to the pressure transducer.

By way of illustration, the tube 10 may be provided with an axial lengthof approximately 4.5 inches and with an external diameter ofapproximately threequarters of an inch. The thickness of the tube 10 maybe approximately 0.06 inches and the distance between the axialpositions 30 and 32 may be approximately 3.5 inches. The axial positions30 and 32 may be equally spaced from the respective ends 18 and 20 ofthe tube. The rod 12 is also provided with a length in the order of 4.5inches and is provided with an external diameter in the order of 0.630inches. The grooves 24 and 26 are provided with a radius in the order of0.030 inches and are respectively separated from the ends of the rod bya distance in the order of O. l 0 inches. The distances between the endsof the rod 12 and the axial positions 36 and 38 are approximately 0.75inches. The bores 50 and 56 are provided with suitable diameters in theorder of 0.060 inches.

The pressure transducer illustrated in FIG. 1 and described aboveoperates to measure pressure by indicating the value of the capacitor 42formed between the conductive coatings 40 and 44. For example, thepressure transducer may be disposed in sea water to measure the pressureof the sea water. The pressure of the sea water causes forces to beimposed in a radial direction on the transducer so that the portion oftube 10 between the axial positions 30 and 32 is compressed toward theexternal periphery of the rod 12. The movement of the tube 10 toward therod 12 in the area between the axial positions 30 and 32 is dependentupon the pressure imposed upon the tube. The value of the capacitor ismeasured at each instant to indicate the pressure imposed upon the tube.The pressure transducer constituting this invention is advantageous foruse in adverse environments such as sea water since the pressuretransducer is completely sealed so that the sea water cannot enter intothe pressure transducer and affect the operation of the transducer.

The space between the conductive coatings 40 and 44 is preferably avacuum so that the dielectric constant of the capacitor 42 formed by theconductive coatings 40 and 44 will be substantially uniform andrelatively high. However, air or any other gas providing a substantiallyuniform dielectric can also be disposed between the conductive coatings40 and 44 without affecting the operation of the pressure transducer. Ifdesired, other dielectric materials than air or gas may also be disposedin the space between the conductive coatings 40 and 44 depending uponthe use desired for the pressure transducer.

The embodiment illustrated in FIG. I and described above is particularlyadapted to-be used for measuring relatively high pressures. For example,the pressure transducer is adapted to measure the pressure of sea waterat considerable depths below the surface of the water. Even at suchrelatively high pressures, the pressure transducer is able to respondaccurately since the curved configurations of the tube and the rod 12cause these members to withstand relatively high pressures and toprovide linear response characteristics with changes in pressure.

If desired, the outer surface of the tube 10 may be coated with aconductive material such as platinum to serve as an electrical shieldfor preventing the operation of the capacitor 42 from being affected byexternal parameters. This conductive coating is illustrated at 60 inFIG. 1. This is not necessary when the pressure transducer is disposedin sea water since the sea water is conductive and serves as anelectrical shield. However, it may be desirable to platinize the outerperiphery of the tube 10 or to provide an external shieldaround the tubewhen the pressure transducer is used in other environments, particularlywhen the environments are not electrically conductive.

The transducing capacitor 42 may be included in a circuit illustrated ona schematic basis in FIG. 2. The construction and operation of thiscircuit are disclosed in detail in copending application Ser. No.501,731 filed Oct. 22, 1965, by me and assigned of record to theassignee of record of this application. The transducing capacitor 42 isconnected to a reference capacitor 70 having a known capacitive value.The terminal of the reference capacitor 70 is connected to a terminal ofa source 72 of reference potential, and the common terminal between thecapacitors 42 and 70 is connected to an input terminal of an operationalamplifier 74. Second terminals of the potential source 72 and theoperational amplifier 74 are grounded.

The output terminal of the amplifier 74 is connected to a terminal 76. Aterminal 78 is connected to the terminal common to a pair of resistors80 and 82, the resistor 82 being adjustable in value. The output isobtained between the terminal 78 and a grounded terminal 84. Theresistors 80 and 82 are in series with the capacitors 42 and 70 to forman electrical bridge. An input voltage may be considered as beingintroduced to a first pair of diagonally opposite terminals in thebridge, and an output voltage may be considered as being obtained from asecond pair of diagonally opposite terminals in the bridge.

The operational amplifier is provided with a very high impedance andideally would be provided with an infinite impedance. Because of this,the common terminal between the capacitor 42 and 70 may be considered asgrounded. Since both input terminals of the amplifier 74 may then beconsidered as grounded, the effects of stray capacitances in the circuitshown in FIG. 3 are minimized. This is discussed in detail in copendingapplication Ser. No. 501,731. By minimizing the effects of straycapacitances, the voltage produced between the terminals 78 and 84provides an accurate indication of the value of the transducingcapacitor 42.

Furthermore, at a pressure of 0, a capacitive value would still existbetween the conductive coatings 40 and 44 defining the transducingcapacitor 42 so that the reactance of the capacitor would be differentfrom 0. The resistors 80 and 82 are included in the circuit shown inFIG. 3 to form a bridge with the capacitors 42 and 70 so that thevoltage across the capacitor 42 for Cs K M where C the value of thecapacitor 42; K a constant d=d the distance between the conductivecoatings 40 and 44. As is well known,

X =l/2rrf C where X, the reactance of the capacitor 42; and f thefrequency of the signal introduced to the capacitor 42.

Substituting in equation (2) the value of C in equation x,- 1/2" f-d/K,-

The ratio between the reactance X of the transducing capacitor 42 andthe reactance X n of the reference capacitor may now be expressed as:

d a i 'fl a 1 K1 where C the value of the reference capacitor 70. SinceC is a constant,

X X K d, where K a constant.

In this way, the ratio between the reactances of the transducingcapacitor 42 and the reference capacitor 70 is linearly related to thedistance between the conductive coatings 40 and 44 of the transducingcapacitor. Since the distance between the conductive coatings 40 and 44is linearly related to the pressure imposed upon the tube 10 relative tothe pressure on the rod 12, the ratio between the reactances of thetransducing capacitor 42 and the reference capacitor 70 is linearlyrelated to such pressure.

The embodiment illustrated in FIGS. 3 and 4 also uses a pair of membersand 102 which are preferably formed from quartz. The members 100 and 102are perferably disposed in a planar configuration and are uniformlyspaced from each other in the planar configuration by a relatively smalldistance such as 0.005 inches. Conductive coatings 104 and 106 arerespectively disposed on the contiguous surfaces of the members 100 and102 to define the plates of a capacitor generally indicated at 108. Theconductive coatings 104 and 106 are preferably provided with aconfiguration such as a circular configuration and are preferablydisposed at the central positions of the contiguous surfaces on themembers 100 and 102. Preferably the diameter of the coatings 104 and 106is fairly small relative to the dimensions of the contiguous surfaces onthe members 100 and 102. For example, the diameter of the conductivecoatings 104 and 106 may be approximately one-third of the totaldiameter of the contiguous surfaces on the members 100 and 102.

As will be seen in FIG. 4, the conductive plate 104 is provided with aconductive handle 112 which extends in a suitable direction and secondas radially from the conductive coating 104 at one end of the coating.An electrical lead 114 is connected to the conductive handle 112 at theouter end of the handle. In like manner, a conductive handle 116 extendsradially from the conductive coating 106 in a direction diametricallyopposed to the handle 112. An electrical lead 118 is connected to theconductive handle 116 at the outer end of the handle. Since the handles112 and 116 are diametrically opposed, a minimal capacitive relationshipexists between the handles. In this way, the value of the capacitor 108is affected essentially only by the distance of the conductive coatings104 and 106 from each other.

A thin conductive coating 120 is disposed on the surface of the member100 facing the member 102. The conductive coating 120 has essentially adoughnutshaped configuration which surrounds the conductive coating 104and the handle 112. The inner periphery of the conductive coating 120 isseparated from the outer periphery of the conductive coating 104 and thehandle 112 by a relatively small distance. In like manner, a conductivecoating 122 having the configuration of the conductive coating 120 isprovided on the same surface of the member 102 as the conductive coating106 and is disposed in contiguous and surrounding relationship to thecoating 106 and the handle 116. The conductive coatings 120 and 122constitute the plates of a shielding capacitor generally indicated at124.

The pressure transducer shown in FIGS. 3 and 4 is adapted to be used formeasuring low pressures. For example, the pressure transducer may beuseed in an airplane to measure the pressure of the atmosphere atdifferent elevations so as to indicate on an accurate and sensitivebasis the elevation of the airplane above sea level. When the pressuretransducer is used to measure low pressures, one of the members 100 and102 may be disposed in a fixed configuration and the other member may beoperated as a diaphragm in accordance with variations in the pressureapplied to the member to vary the distance between the members 100 and102. Since the change in pressure between the members 100 and 102 causesthe distance between the conductive plates-104 and 106 to vary, thecapacitor 108 formed by the conductive plates 104 and 106 provides adirect indication of the pressure imposed upon one of the members suchas the member 100 in accordance with the value of the capacitor at eachinstant. For example, a change of lbs. per square inch in pressure mayproduce a change of 0.003 inches between the conductive plates 104 and106.

The conductive plates 104 and 106 are respectively disposed at thecenters of the adjacent surfaces on the members 100 and 102 for severalimportant reasons.

- One reason is that the movement of the members 100 and 102 relative toeach other is greater with changes in pressure at the center of themembers than at the periphery of the members. Another reason is that theshielding capacitor 124 can then be disposed around the transducingcapacitor 108 to prevent fringe lines of force around the periphery ofeach of the conductive coatings 104 and 106 from travelling to the otherconductive coating. Since such fringe lines do not travel in straightpaths, they prevent the value of the capacitor 108 from changinglinearly with changes in the pressure imposed upon one of the members100 and 102. These fringe lines are illustrated in broken lines at 130in FIG. 3. i

The conductive plates 120 and 122 are preferably connected to each otherto receive a suitable reference potential such as ground. Since theconductive plates 104 and 120 are disposed in contiguous relationship, acapacitor 132 is produced between these plates. Similarly, a capacitor134 is produced between the plates 106 and 122. On this basis, acapacitive network similar to that illustrated in FIG. 7 is produced bythe arrangement shown in FIGS. 3 and 4. The capacities 132 and 134 inthis network do not appreciably affect the measurement of thetransducing capacitor 108 since they are connected in substantiallysymmetrical relationship to the plates of the capacitor 108 and theirvalues are substantially equal and relatively low.

Preferably the capacitive arrangement shown in FIGS. 3 and 4 is disposedwithin a shield to limit the production of other capacitive effectsresulting from fringe lines of force. For example, some capacitiveeffect would be produced between the handles 112 and 116 if a shieldwere not disposed around the unit shown in FIG. 3 and 4. Some capacitiveeffect would also be produced illustratively between the conductivecoatings 106 and 120 and between the conductive coatings 104 and 122 ifthe unit shown in FIGS. 3 and 4 were not disposed within a shield.

The pressure transducer shown in FIGS. 3 and 4 may be made by a methodconstituting a novel feature of this invention. As illustrated in FIGS.5 and 6, a plurality of platinum wires 200 may be disposed between themembers 100 and 102 to provide the desired spacing between the members.For example, when a spacing of approximately 0.005 inches is desiredbetween the planar surfaces of the members 100 and 102, the platinumwires 200 may be provided with a thickness of approximately 0.005inches. As illustrated in FIG. 6, the platinum wires may actually bedrawn through an opening 202 in a flange 204 on the member 100 andthrough an opening 206 in a flange 208 on the member 102. The members100 and 102 may then be fused as at 210 to seal the members and tomaintain the desired spacing of 0.005 inches between the members. Afterthe members have been fused, the wires 200 may be withdrawn from thespace between the members 100 and 102 without affecting the spacedrelationship between the members.

The flanges 202 and 206 also perform another function. As may be seen inFIG. 6, the conductive handle 116 is extended through the bore 206 inthe flange 208 to a position external to the flange, and an electricalconnection is made at this external position between the extended handleand the electrical lead 118. Similarly, the conductive handle 112 isextended on the member 102 so as to pass through the bore 202 to a potheexternal position. In this way, electrical connections can be easilymade to the conductive coatings 104 and 106 defining the transducingcapacitor 108.

Although this application has been disclosed and illustrated withreference to particular application, the principles involved aresusceptible of numerous other applications which will be apparent topersons skilled in the art. This invention is, therefore, to be limitedonly as indicated by the scope of the appended claims.

What is claimed is:

1. In combination for use in a pressure transducer,

a hollow tube made from a chemically inert, electrically insulatingmaterial having substantially linear stress-strain characteristics andcapable of withstanding relatively low and high temperatures and havinga relatively low temperature coefficient of expansion and capable ofwithstanding considerable pressure, the hollow tube having a pair ofopposite ends to define a closure;

a rod made from a chemically inert, electrically insulating materialhaving substantially linear stressstrain characteristics and capable ofwithstanding relatively low and high temperatures and having arelatively low temperature coefficient of expansion and capable ofwithstanding considerable pressures, the rod having a pair of oppositeends and a curved external surface between the opposite ends, the curvedexternal surfaces on the rod corresponding to-the curved internalsurface in the tube;

the rod beingdisposed within. the tube and being sealed to the tube atthe opposite ends, the rod 1 being snugly disposed against the tubeswithin the opposite ends and being tapered slightly at an intermediateposition between the opposite ends relative to the tube to have a slightspacing from the tube;

the external surface of the rod and the internal surface of the tubebeing coated with an electrically conductive material at theintermediate positions between the opposite ends to define first anddsecond plates of a capacitor;

there being a substantially uniform dielectric in the spacing betweenthe tube and the rod; and

means for providing for an indication of variations in the value of thecapacitor in accordance with variations in the spacing between the firstansecond plates.

2. The combination set forth in claim 1 wherein the rod and the tube aremade from quartz and are substantially cylindrical.

3. The combination set forth in claim 1 wherein the hollow tube has anexternal surface which is coated with a conductive material to provideexternal shielding for the capacitor defined by the hollow tubeand therod.

4. In combination for measuring variations in pressure,

a first quartz member having a first surface;

a second quartz member having a second surface;

first electrically conductive material on the first surface of the firstquartz member;

second electrically conductive material on the second surface of thesecond quartz member;

the first and second quartz members being sealed to each other with thefirst and second surfaces having a particular spacing relative to eachother to define plates of a capacitor;

one of the first and second quartz members being movable relative to theother quartz member in response to variations in pressure to produce avariable value for the capacitor in accordance with such variablepressure;

first and second electrical leads respectively connected to the firstand second electrically conductive material to provide outputindications of the variable value of the capacitor;

an electrical shield enveloping the first and second quartz members; and

the opposite extremities of the first and second quartz members beingfused to produce the seal between the members.

5. In combination for measuring variations in pressure,

a first quartz member having a particular configuration and defined byat least one extremity and having a first surface in the particularconfiguration;

a second quartz member having the particular configuration and definedby at least one extremity and having a second surface in the particularconfiguration; v

the extremities of the first and second quartz members being sealed toeach other with the first surface on the first quartz member and thesecond surface on the second quartz member in contiguous relationship; I

a first thin electrically conductive coating uniformly disposed on thefirst surface of the first quartz member;

a second thin electrically conductive coating unifo'rmly disposed on thesecond surface of the second quartz member;

a first electrical lead extending from the first thin electricallyconductive coating;

a second electrical lead extending from the second thin electricallyconductive coating;

an electrical shield being provided for the first and second quartzmembers; and

the opposite extremities of the first and second quartz members beingfused to provide the seal.

6. In combination for use in a pressure transducer:

a first member made from a chemically inert, electrically insulatingmaterial having substaiitially linear stress-strain characteristics andcapable of withstanding relatively low and high temperatures and havinga relativelylow temperature coefficient of expansion and capable ofwithstanding considerable pressures, the first member having aparticular configuration and at least one extremity and having a firstsurface;

a second member made from a chemically inert, electrically insulatingmaterial having substantially linear stress-strain characteristics andcapable of withstanding relatively low and high temperatures and havinga relatively low temperature coefficient of expansion and capable ofwithstanding considerable pressures, the second member having theparticular configuration and at least one extremity and having a secondsurface;

the first and second members being sealed to each other at theirextremities with the first and second surfaces being disposed incontiguous and substantially uniformly spaced relationship;

and second surfaces;

an electrical shield enveloping the first and second members; and

the extremities of the first and second members being fused to definethe shields.

III k '1'

1. In combination for use in a pressure transducer, a hollow tube madefrom a chemically inert, electrically insulating material havingsubstantially linear stress-strain characteristics and capable ofwithstanding relatively low and high temperatures and having arelatively low temperature coefficient of expansion and capable ofwithstanding considerable pressure, the hollow tube having a pair ofopposite ends to define a closure; a rod made from a chemically inert,electrically insulating material having substantially linearstress-strain characteristics and capable of withstanding relatively lowand high temperatures and having a relatively low temperaturecoefficient of expansion and capable of withstanding considerablepressures, the rod having a pair of opposite ends and a curved externalsurface between the opposite ends, the curved external surfaces on therod corresponding to the curved internal surface in the tube; the rodbeing disposed within the tube and being sealed to the tube at theopposite ends, the rod being snugly disposed against the tubes withinthe opposite ends and being tapered slightly at an intermediate positionbetween the opposite ends relative to the tube to have a slight spacingfrom the tube; the external surface of the rod and the internal surfaceof the tube being coated with an electrically conductive material at theintermediate positions between the opposite ends to define first andsecond plates of a capacitor; there being a substantially uniformdielectric in the spacing between the tube and the rod; and means forproviding for an indication of variations in the value of the capacitorin accordance with variations in the spacing between the first andsecond plates.
 2. The combination set forth in claim 1 wherein the rodand the tube are made from quartz and are substantially cylindrical. 3.The combination set forth in claim 1 wherein the hollow tube has anexternal surface which is coated with a conductive material to provideexternal shielding for the capacitor defined by the hollow tube and therod.
 4. In combination for measuring variations in pressure, a firstquartz member having a first surface; a second quartz member having asecond surface; first electrically conductive material on the firstsurface of the first quartz member; second electrically conductivematerial on the second surface of the second quartz member; the firstand second quartz members being sealed to each other with the first andsecond surfaces having a particular spacing relative to each other todefine plates of a capacitor; one of the first and second quartz membersbeing movable relative to the other quartz member in response tovariations in pressure to produce a variable value for the capacitor inaccordance with such variable pressure; first and second electricalleads respectively connected to the first and second electricallyconductive material to provide output indications of the variable valueof the capacitor; an electrical shield enveloping the first and secondquartz members; and the opposite extremities of the first and secondquartz members being fused to produce the seal between the members. 5.In combination for measuring variations in pressure, a first quartzmember having a particular configuration and defined by at least Oneextremity and having a first surface in the particular configuration; asecond quartz member having the particular configuration and defined byat least one extremity and having a second surface in the particularconfiguration; the extremities of the first and second quartz membersbeing sealed to each other with the first surface on the first quartzmember and the second surface on the second quartz member in contiguousrelationship; a first thin electrically conductive coating uniformlydisposed on the first surface of the first quartz member; a second thinelectrically conductive coating uniformly disposed on the second surfaceof the second quartz member; a first electrical lead extending from thefirst thin electrically conductive coating; a second electrical leadextending from the second thin electrically conductive coating; anelectrical shield being provided for the first and second quartzmembers; and the opposite extremities of the first and second quartzmembers being fused to provide the seal.
 6. In combination for use in apressure transducer: a first member made from a chemically inert,electrically insulating material having substantially linearstress-strain characteristics and capable of withstanding relatively lowand high temperatures and having a relatively low temperaturecoefficient of expansion and capable of withstanding considerablepressures, the first member having a particular configuration and atleast one extremity and having a first surface; a second member madefrom a chemically inert, electrically insulating material havingsubstantially linear stress-strain characteristics and capable ofwithstanding relatively low and high temperatures and having arelatively low temperature coefficient of expansion and capable ofwithstanding considerable pressures, the second member having theparticular configuration and at least one extremity and having a secondsurface; the first and second members being sealed to each other attheir extremities with the first and second surfaces being disposed incontiguous and substantially uniformly spaced relationship; the firstand second surfaces being coated with an electrically conductivematerial to define opposite plates of a capacitor having a valuedependent upon the spacing between the first and second surfaces; firstand second leads respectively connected to and extending from theelectrical coatings on the first and second surfaces; an electricalshield enveloping the first and second members; and the extremities ofthe first and second members being fused to define the shields.